The Role of ZnO as a Dopant and an Intergranular Phase in the Electrical Properties of Ca0.6Sr0.4TiO3 Ceramics

ZnO was introduced into Ca0.6Sr0.4TiO3 ceramics as a dopant and an intergrangular phase in this research, followed by detailed structure characterization, energy storage performance analysis, and electrical behavior studies. The results revealed that the existence of ZnO as a dopant led to the decrease of conduction activation energy and the deterioration of energy storage behavior, while appropriate introduction of ZnO as an intergranular phase resulted in the increase of conduction activation energy and the optimization of energy storage performance. Additionally, the inverse relation between interfacial polarization and energy storage performance was observed in this study. Finally, an increased energy storage density of 1.16 J/cm3 was achieved in 1 mol% ZnO-added Ca0.6Sr0.4TiO3 ceramics.

Limitations in the Grain Boundary Processing of the Recycled HDDR Nd-Fe-B System

Fully dense spark plasma sintered recycled and fresh HDDR Nd-Fe-B nanocrystalline bulk magnets were processed by surface grain boundary diffusion (GBD) treatment to further augment the coercivity and investigate the underlying diffusion mechanism. The fully dense SPS processed HDDR based magnets were placed in a crucible with varying the eutectic alloys Pr68Cu32 and Dy70Cu30 at 2–20 wt. % as direct diffusion source above the ternary transition temperature for GBD processing followed by secondary annealing. The changes in mass gain was analyzed and weighted against the magnetic properties. For the recycled magnet, the coercivity (HCi) values obtained after optimal GBDP yielded ~60% higher than the starting recycled HDDR powder and 17.5% higher than the SPS-ed processed magnets. The fresh MF-15P HDDR Nd-Fe-B based magnets gained 25–36% higher coercivities with Pr-Cu GBDP. The FEG-SEM investigation provided insight on the diffusion depth and EDXS analysis indicated the changes in matrix and intergranular phase composition within the diffusion zone. The mechanism of surface to grain boundary diffusion and the limitations to thorough grain boundary diffusion in the HDDR Nd-Fe-B based bulk magnets were detailed in this study.

An Experimental Study of the Failure Mode of ZnO Varistors Under Multiple Lightning Strokes

In this study, in order to explore the failure mode of ZnO varistors under multiple lightning strokes, a five-pulse 8/20 μs nominal lightning current with pulse intervals of 50 ms was applied to ZnO varistors. Scanning electron microscopy (SEM) and X-ray diffractometry (XRD) were used to analyze the microstructure of the material. The failure processes of ZnO varistors caused by multiple lightning impulse currents were described. The performance changes of ZnO varistors after multiple lightning impulses were analyzed from both macro and micro perspectives. According to the results of this study’s experiments, the macroscopic failure mode of ZnO varistors after multiple lightning impulses involved the rapid deterioration of the electrical parameters with the increase of the number of impulse groups, until destruction occurred by side-corner cracking. The microstructural examination indicated that, after the multiple lightning strokes, the proportion of Bi in the crystal phases was altered, the grain size of the ZnO varistors became smaller, and the white intergranular phase (Bi-rich grain boundary layer) increased significantly. The failure mechanism was thermal damage and grain boundary structure damage caused by temperature gradient thermal stress, generated by multiple lightning currents.